As for AT&T and Verizon, the two biggest carriers both recently did away with overage fees but -- unlike Sprint and T-Mobile -- still throttle speeds after a certain point. AT&T(T) announced it would stop charging people for data overage fees. Instead of hitting customers with fees for going over data quotas, it will automatically reduce wireless speeds to 2G. Customers can pay for more data at faster speeds, if they so choose.

Meanwhile, Verizon(VZ) recently introduced a pre-paid "Safety Mode" feature, which allows users to pay a set overdraft fee before quotas are met.

Both of these strategies are meant to provide a pseudo-unlimited data plan, but Sprint and T-Mobile's latest flat-fee update may be more appealing for customers who want simplicity and don't care as much about video streaming quality.

While T-Mobile will keep its existing data plans around, Legere said during a press conference the plan is to eventually retire them, but existing customers will be able to stay in their plans if they choose.

The company likened the move to what happened when the carriers moved away from monthly talk "minutes" to "unlimited" options.

"This is not just a rate plan for us," CEO John Legere said on a conference call Thursday morning. "It simplifies the whole concept of how you deal with T-Mobile."